The present invention relates to a master cylinder for supplying a brake fluid to a brake apparatus of an automobile or the like.
According to a master cylinder of a related art, there is provided a constitution in which by supplying a large volume of a brake fluid at an initial stage of operation (carrying out a so-called fast fill) when the brake fluid is supplied to a brake apparatus such as a disk brake or a drum brake, an ineffective fluid amount at an initial stage of a stroke is compensated for, and as a result, a pedal stroke can be shortened.
The master cylinder is provided with a stepped cylinder having a large diameter cylinder portion and a small diameter cylinder portion; a stepped piston having a large diameter piston portion slidably inserted into the large diameter cylinder portion of the stepped cylinder and a small diameter piston portion slidably inserted into the small diameter cylinder portion of the stepped cylinder; and a reverse-flow-checking opening and closing portion for partitioning the inside of the stepped cylinder into a large diameter pressurizing chamber on the large diameter piston portion side and a small diameter hydraulic chamber communicating with a brake apparatus on the small diameter piston portion side, and permitting flow of the brake fluid only from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side, wherein when a volume of the large diameter pressurizing chamber is reduced by a sliding movement of the stepped piston toward the small diameter hydraulic chamber side, the reverse-flow-checking opening and closing portion is opened to supply the fluid from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side.
The master cylinder is provided with a control valve device for opening the reverse-flow-checking opening and closing portion in response to a reduction in a volume of the large diameter pressurizing chamber caused by the sliding movement of the stepped piston toward the small diameter hydraulic chamber side to thereby supply the fluid from the large diameter pressurizing chamber side to the small diameter hydraulic chamber side, and for releasing a hydraulic pressure in the large diameter pressurizing chamber to a reservoir side such that the hydraulic pressure in the large diameter pressurizing chamber is gradually reduced in accordance with a rise in a hydraulic pressure in the small diameter hydraulic chamber (for example, refer to A Japanese Patent Laid-Open Publication No. 2002-321609).